1. Field of the Invention
This invention relates to a file-allocation control system for use in computer systems having a plurality of mass storage units.
2. Description of the Related Art
The job management function of the operating system allows a user program which requests allocation of the file space to a plurality of resident or public volumes to designate not specified volume names but a volume group consisting of a number of volumes in a job control statement.
Once the user program requests such allocation of file space by designating a volume group, the job management function will select free space and allocate it to the files of the user-program according to the following rules as disclosed in "ACOS-4/XVP Job Management Reference Manual, DDA81E-2, NEC CORPORATION, 1992, pp. 6-90 to 6-96".
(1) Change the start volume of checking cyclically.
(2) Allocate the volumes in decreasing order of space available.
(3) Allocate the volumes in increasing order of I/O load into/from them.
In special circumstance may be adopted the rule:
(4) Always check the volumes in the same sequence.
These rules are effective for a volume group consisting of disk units of similar performance characteristics, e.g. access speeds.
In recent computer systems however magnetic and electronic disk units of different performances are introduced. The mixed construction of such disk units of different performances included in a volume group may not allow according to circumstances the above-mentioned rules to be effective because the processing times are greatly different among the different types of disk units to which the files are allocated.
The problem mentioned above can be solved by management of disk units for forming them into volume groups of different speed levels. In this case it is needed for the user program to previously recognize what speed level of disk units individual volume groups are composed of and notably to designate what volume group should be used.